Portable asphalt heaters, also referred to as asphalt carriers, are typically used in the building or repair of roads or other paved surfaces. Asphalt is typically a mixture of aggregates and binder, which may be applied in a layer on top of a base so as to form the paved surface. Aggregates may include crushed rock, sand, gravel and other materials. To bind the aggregate into a cohesive mixture, a binder is used, for example, bitumen. When asphalt is cooled to ambient temperatures, it forms a hard surface for supporting a load.
In order to create a substantially level asphalt surface, it is necessary to heat the asphalt to specific temperatures to facilitate spreading of the asphalt over a surface so as to create a substantially uniform layer. For example, depending on the particular type of asphalt used, the asphalt may need to be heated to a range of approximately 200° F. to 250° F. (or 93° C. to 121° C.) so as to render it malleable enough for spreading. It is therefore often required to maintain the asphalt in a portable asphalt heater or carrier, which carrier may be driven to the location of the paving project. Because the load of asphalt which may need to be transported to a project site may be quite heavy, for example in the range of eight metric tonnes, and because such transportation may often be accomplished by means of a truck, such asphalt carriers may be designed with a sufficiently lowered centre of gravity so as to maintain stability of the asphalt carrier vehicle when it is travelling at normal road or highway speeds, even while carrying a full asphalt load.
Furthermore, it is desirable for such asphalt carriers to be as efficient as possible at heating the asphalt and maintaining the asphalt at a given temperature, so as to conserve the fuel required to heat the asphalt, thereby reducing both the cost and the environmental impact of paving projects. Typical asphalt heaters may be fueled by diesel, propane or gasoline, for example.
In prior art asphalt carriers and heaters, of which the applicant is aware, there have been several attempts to make such equipment more energy-efficient. For example, in U.S. Pat. No. 8,465,225 by inventors Groulx et al (the '225 patent), a portable asphalt recycling and heat management unit comprises a seamless, vacuum-formed one-piece combustion chamber that defines a fuel incubator disposed therein.
The unit further includes a heat accumulator operably coupled to the combustion chamber and a hopper assembly. The apparatus in the '225 patent further includes a heat distribution system in communication with the heat accumulator and the hopper assembly to provide heat to the hopper assembly for recycling used asphalt or for maintaining a mixture of asphalt for use in asphalt repairs. The portable asphalt recycling unit of the '225 patent is designed to be mounted on a trailer, and has an overall asymmetric geometry.
In U.S. Pat. No. 4,695,186 by inventor King (the '186 patent), an asphalt handling apparatus includes a hopper portion with an elongated trough, having a generally V-shaped cross-section. A pair of bifold doors selectively cover the opening to the hopper. The hopper heating portion includes an enclosed heat transfer medium first chamber disposed immediately below the V-shaped trough section and in direct contact therewith. The first chamber includes sloping wing sections and a deeper central section communicating therewith. A U-shaped burner channel is disposed substantially horizontally within the central section with the gas burner along the first arm and an exhaust stack extending upwardly from a second arm. An elongated electrical heating element is disposed between the arms. The liquid tack material dispensing portion includes an elongated second chamber located alongside the central section of the hopper heating portion. The second chamber includes tubing therein communicating with the central section of the hopper heating portion. A valve mechanism communicates within an outlet of the second chamber. A cleaning fluid reservoir communicates with the valve mechanism. Disposed within the hopper portion is a screw conveyor for moving the asphalt through the hopper towards the exit of the hopper.
In U.S. Pat. No. 3,577,976 by inventor Heller (the '976 patent), a unit for storing and maintaining asphalt At an elevated temperature includes a storage compartment that is enveloped within the body of heated air flowing at a controlled rate and the outer wall bounding the passage for this convection flowing heated air is insulated against heat loss. The enveloping heated air results in a heat gradient around the heated asphalt, minimizing heat loss. The interior of the asphalt storage unit includes an inverted V-shaped structure extending from the floor of the storage compartment so as to distribute heat from heated air flowing underneath the inverted V-shaped structure, reducing the internal storage capacity of the asphalt storage unit.
In U.S. Pat. No. 5,120,217 by inventors O'Brien et al (the '217 patent), a unit for heating initially solid asphalt material to provide the asphalt in a condition suitable for application includes an inner enclosure defining a volume for containing the asphalt to be heated, an outer enclosure surrounding and spaced from the inner enclosure to define a space beneath the inner enclosure and passages for heated air flow around the walls of the inner enclosure, a screw disposed in an open top channel at the floor of the inner enclosure to move heated material, an opening in the inner enclosure floor in communication with the passage in the outer enclosure floor for delivery of heated asphaltic material moved by the screw to the unit's exterior, heating chambers projecting upwardly from the floor of the inner enclosure above the heating sources to provide regions through which hot air rises from the sources, and flues extending transversely from the upper portions of the heating chamber to the end walls of the inner enclosure for conducting the heated air from the heating chambers to the aforementioned passages. The inner enclosure for containing the asphalt includes an approximately V-shaped geometry.